An electoral worker marks the finger of a Nigerian woman at a polling station during the presidential elections in Daura on April 16, 2011.

Nigeria's incumbent leader Goodluck Jonathan appeared on track to keep his job, early results from Saturday's presidential elections showed, although there were concerns over voting irregularities.

Figures posted by Nigeria's Independent National Electoral Commission on its website showed that with 28 of the country's 36 states counted, Jonathan had 19 million votes compared to main challenger Muhammadu Buhari's 9 million, CNN said.

There has been no official confirmation of the result, but the margin of the lead indicates Jonathan will achieve victory without the need for a runoff vote.

There were complaints of irregularities, including reports of underage voting and suspicious voting patterns, but these were not expected to affect the final outcome, observers said.

Jonathan was credited with winning 99 percent of the vote in his home state Bayelsa, in the southern Niger Delta region. Nearby states also reported similar landslides.

"Figures of 95 percent and above for one party suggest that these are fabricated figures and, personally, they worry me because they pose serious questions on the credibility of the election," Jibrin Ibrahim of the Centre for Democracy and Development told AFP, as cited by the BBC.

The results sparked violence in the country's Mainly-Muslim north, where Jonathan — a Christian who took office last year when his predecessor Umaru Yar'Adua became terminally ill — has struggled to win support.

But the BBC said there was a "sense of relief and jubilation that the vote and count have been relatively calm, unlike in past years."

Jonathan's camp said it would hold off on declaring victory until officials confirmed the result.

"This is no time for triumphalism. It is a time for deep reflection, for strengthening the bond of our union and for all of us to work together," Oronto Douglas, a senior advisor to Jonathan, told Reuters.

The presidential elections are Nigeria's fourth since the country reverted from military rule 12 years ago. Previous votes have been marred by claims of corruption and violence.

Analysts say a stable election will increase confidence in Nigeria as it tackles graft, security and infrastructure problems that have stymied its ability to capitalize on the vast incomes it generates as Africa's biggest oil exporter.